Devices utilizing a photonic crystal have been developed for the purpose of achieving high performance, small size and low cost in the field of optical communication devices such as an optical multiplexer/demultiplexer which is used for the wavelength division multiplexing communication (WDM). A photonic crystal is a dielectric body having an artificial cyclic structure. The cyclic structure is usually formed by arranging areas (modified refractive index areas) having a refractive index different from that of the dielectric main body cyclically in the dielectric main body. The cyclic structure creates a band structure with respect to light energy in the crystal, so that an energy region or regions are formed in which light cannot propagate. Such an energy region is called the “photonic band gap (PBG)”. The energy region (or a wavelength band) in which the PBG is formed is determined depending on the refractive index of the dielectric and the cycle of the cyclic structure.
Patent Document 1 discloses a two-dimensional photonic crystal having a main body (or slab) provided with modified refractive index areas arranged cyclically, in which a linear defect is provided to the cyclic arrangement so as to form a waveguide, and a point-like defect is provided to the cyclic arrangement beside the waveguide so as to form a resonator. This two-dimensional photonic crystal has two functions. One is a demultiplexer for extracting light having a wavelength equal to the resonance wavelength of the resonator from light having various wavelengths propagating in the waveguide to the outside. Another function is a multiplexer for introducing the light from the outside into the waveguide.
In addition, recently, it is studied to use the two-dimensional photonic crystal as a thermal radiation light source. Non-Patent Document 1 describes a two-dimensional photonic crystal 10 as illustrated in FIG. 1(a), in which holes 12 are arranged cyclically in a slab 11 having a quantum well structure constituted of a plurality of laminated semiconductor plates 111, 112, . . . made of different semiconductor materials, and a point like part of the holes are omitted to form a point-like defect resonator 13. As illustrated in FIGS. 1(b) and 1(c), every hole 12 is disposed on a lattice point 141 of a triangular lattice on an upper surface of the slab, and is disposed on a lattice point 142 on a lower surface just below the barycenter of every regular triangle of the upper surface triangular lattice. Further, between the upper surface and the lower surface, every hole 12 on the upper surface extends from the upper lattice point 141 aslant in three directions toward three lower lattice points 142 that are closest to the upper lattice point 141. Every hole 12 on the lower surface extends from the lower lattice point 142 aslant in three directions toward three upper lattice points 141 that are closest to the lower lattice point 142. When the two-dimensional photonic crystal 10 is heated, transition of electrons or holes occurs between discrete energy levels (subbands) formed in the quantum well so as to generate light having the wavelength corresponding to the energy difference. Intensity of this light is amplified by the point-like defect resonator 13, and the light is emitted to the outside of the two-dimensional photonic crystal 10.
A usual thermal radiation source emits a wide band of infrared rays similar to the black body spectrum. Therefore, in order to use the thermal radiation source for a spectral analysis of gas contents or the like, it is necessary to extract a desired wavelength from the band by using a filter. In contrast, a thermal radiation light source using the two-dimensional photonic crystal can inherently emit only light having a desired wavelength, so it is expected to improve the energy utility efficiency.
[Patent Document 1] Unexamined Japanese Patent Publication No. 2001-272555 ([0023]-[0027], [0032], FIGS. 1, and 5-6)
[Non-Patent Document 1] Keita MOCHIZUKI et al. “Analysis of Thermal Radiation Spectrum from Two-dimensional Photonic Crystal Slab with Quantum Well Having Transition between Subbands”, 2006 Autumn 67th Joint Symposia on Applied Physics, third part issue, Japan Society of Applied Physics, Aug. 29, 2006, lecture number 31p-ZD-12